JPH01133377A - Image sensor - Google Patents

Abstract

PURPOSE:To obtain an image sensor having fast speed responsiveness, stable characteristics, easy manufacture and a low cost by forming a photoconductive film of TlI being thick in the sensor having the photoconductive film in which its conductivity is varied according to the irradiation of a light. CONSTITUTION:A photoconductive film 2 is formed of TlI. The TlI for forming the film 2 is preferably stoichiometrical composition, but may be slightly deviated from it. The film 2 is preferably formed of only TlI, but may contain 5wt.% or less impurity such as Br, In, S, etc. Such a TlI film is normally of a polycrystalline film of TlI. The thickness of the film 2 is generally 0.2-200mum, and particularly approx. 1-20mum. A photoconductive film made of TlI is formed as a thick film by a thick film method, such as a screen printing method or the like. Thus, an image sensor exhibits easy manufacture, high productivity, low cost and excellent photoconductivity.

Description

[Detailed description of the invention] ■ Background of the invention Technical field The present invention relates to an image sensor using a photoconductive film.

Prior art and its problems Image sensors using photoconductive films are used in facsimiles and the like.

Conventionally, materials for photoconductive films include amorphous silicon and Cd5-, which can be made as large as the original size.
CdSe or the like is used, and these photoconductive films are used in contact type image sensors such as complete contact type image sensors or image sensors using an erecting equal-magnification lens.

However, these photoconductive film materials have the following problems.

Amorphous silicon photoconductive film is PIP, NIN%N
Productivity is low because it has a multilayer structure such as I. In addition, since the film is formed using the plasma CVD method, the cost is high;
Moreover, it is difficult to uniformly form a film on a large number of large substrates (A4 size, B4 size, etc.). In general, flakes are likely to occur in the plasma CVD method, making it difficult to obtain a defect-free film.

Also, o2, )! The film tends to become unstable due to surface adsorption of 20 and the like.

The Cd5-CdSe photoconductive film has a photoresponse speed of 8 to 10 m.
Because it is slow at 5ec, it is difficult to read high-speed facsimiles and color documents. Furthermore, it is difficult to obtain a film with constant conversion efficiency, resulting in poor yield.

11 OBJECTS OF THE INVENTION It is an object of the present invention to provide an image sensor that solves the above-mentioned problems, has a fast response speed, stable characteristics, is easy to manufacture, and is low in cost.

1II Disclosure of the invention Such objects are achieved by the invention described below.

That is, the present invention is an image sensor having a photoconductive film whose conductivity changes upon irradiation with light, and wherein the photoconductive film is a thick film formed from T1I.

In addition, the present inventors disclosed in Japanese Patent Application Laid-Open No. 62-73677,
It has been proposed to use thallium halides, such as TlBr and TlCl, as photoconductive elements, but these have poor properties and low sensitivity to red light.

In the present invention, T1I, which has high sensitivity particularly to red-emitting LEDs, is used.
This paper proposes to use the photoconductive film as a photoconductive film.

rv Specific configuration of the invention Hereinafter, a specific configuration of the present invention will be explained in detail.

A preferred embodiment of the image sensor of the present invention is shown in FIGS. 1 and 2.

The image sensor 1 of the present invention shown in FIGS. 1 and 2 includes a transparent conductive film 6 having a light guiding window 10 on a substrate 3;
It has a common electrode 4, a photoconductive film 2 and an individual electrode 5 in this order,
A light source 7 and an erect equal-magnification lens array 8 are provided on the opposite side of the photoconductive film 2 of the substrate 3.

The image sensor 1 guides light emitted from a light source 7 and reflected on the surface of a document 9 to a photoconductive film 2 in a light guide window 10 using a royal equal-magnification lens array 8 to measure the conductivity of the photoconductive film 2. The light guide windows 10 facing each other with the photoconductive film 2 in between
It reads changes in the current generated between the transparent conductive film 6 and the individual electrodes 5 inside, and converts the intensity of reflectance due to the density distribution on the surface of the document 9 into the intensity of the current.

In the present invention, the photoconductive film 2 is formed from T1I.

It is preferable that Tll forming the photoconductive film 2 has a stoichiometric composition, but it may have a somewhat even or odd composition.

Further, it is preferable that the photoconductive film 2 is formed only from Tll, but Br is used as an impurity.

In, S, etc. may be contained in an amount of 5 wt% or less of the total.

Such a T1I film is usually a T1I polycrystalline film.

Further, the film thickness of the photoconductive film 2 is generally 0.2 to 200 μm.
, especially about 1 to 20 μm.

The photoconductive film of the present invention made of T1I is formed as a thick film by a thick film method such as a screen printing method.

Therefore, the image sensor of the present invention is easy to manufacture, has high mass productivity, and is low in cost.

It also exhibits extremely good photoconductivity.

On the other hand, when a thin film method is used to form T1I, for example, when vacuum deposition is performed, only low photosensitivity can be obtained. In this case, heat treatment after film formation improves photosensitivity, but increases the number of steps and reduces productivity.

Furthermore, sputtering causes decomposition of T1I, resulting in only low photosensitivity.

When forming a film by a printing method, a paste is formed using a binder such as ethyl cellulose and a solvent such as terpineol or butyl carbitol, screen printing is performed, and then baking is performed.

The Tll used in the paste may have an average particle size of about 0.1 to 2 μm. Also, 20-70wt in the paste
% may be included.

The firing conditions are 200 to 50 in vacuum or normal pressure.
0.degree. C., more preferably at 250-350.degree. C. in vacuum.
It is preferable to set it as 2 to 3 hours, more preferably 0.5 to 1 hour.

Light from a light source, particularly a red light emitting LED, is absorbed by the surface layer of the T1I film and exhibits photoconductivity. Therefore, even if a film is formed by the thick film method and the film thickness varies, the image sensor characteristics do not vary, and an image sensor with good characteristics can be realized by an easy and inexpensive manufacturing method.

The substrate 3 is not particularly limited as long as it has a high transmittance for light emitted from the light source 7, but it is usually formed of plate glass, quartz, various resins, or the like.

The thickness of the substrate 3 is usually about 0.5 to 3 mm.

The common electrode 4 has a light guide window 10 for guiding reflected light from the original 9 to the individual electrodes 5, and is made of an opaque material to prevent stray light and obtain high resolution, and has the function of a light shielding plate.

The dimensions of the light guide window 10 correspond to the dimensions of the individual electrodes 5, but
It is usually about 50×50 μm to 200×200 μm.

Note that a transparent conductive film, which will be described later, may be used as a common electrode, and a light shielding plate having the above function may be provided separately. In this case, the material of the light shielding plate is metal such as Cr, Mo, or S.
It may also be a non-conductive material such as i.

Further, the material of the common electrode 4 includes Cu, Cr, Ni,
Pt or the like may be used.

The arrangement density of the individual electrodes 5 corresponds to the number of pixels, and is usually 6 to 6.
The number is about 16 pieces/mm.

The materials of the individual electrodes 5 are Cu and Ni.

Cr%pt or the like may be used.

These electrodes may be formed by a thick film method such as a screen printing method, a thin film forming method such as a sputtering method, or a vapor deposition method. When a thin film forming method is used, a pattern may be formed by masking during film formation. Alternatively, after the film is formed, a predetermined pattern may be formed by various types of etching.

A predetermined voltage is applied between the common electrode 4 and the individual electrodes 5, and a current flows between the two electrodes in accordance with the change in the conductivity of the photoconductive film 2.

The transparent conductive film 6 is provided in contact with the common electrode 4 and faces the individual electrodes 5 through the light-receiving portion of the photoconductive film 2, so that the current according to the change in conductivity of the photoconductive film 2 is , which mainly flows between the transparent conductive film 6 and the individual electrodes 5.

As the material of the transparent conductive film 6, ITOlNESA or the like may be used.

As the light source 7, it is preferable to use an LED because it saves space and consumes low current.

In the present invention, since T1I is used as the material of the photoconductive film 2,
From the viewpoint of photosensitivity, it is preferable to use a red-emitting LED, and it is particularly preferable to use a red-emitting LED whose emission spectrum has a wavelength of about 660 nm.

A known erecting equal-magnification lens array 8 may be used;
Moreover, instead of this, a fiber lens array or the like may be used.

3 and 4 show other preferred embodiments of the image sensor of the present invention.

The image sensor 1 shown in these figures has a photoconductive film 2 on a substrate 3, and a common electrode 4 with this photoconductive film 2 in between.
and individual electrodes 5 are provided on the substrate 3.

The structure and operation of each member in this case are the same as those described above in the explanation of FIGS. 1 and 2.

FIGS. 5 and 6 show still other preferred embodiments of the image sensor of the present invention.

The image sensor 1 shown in these figures is of a so-called complete contact type, and does not use an optical system such as an erecting equal-magnification lens array.

The image sensor 1 has a light source 7 on the upper side of the substrate 3, and has a common electrode 4, a photoconductive film 2, a transparent conductive film 6, and an individual electrode 5 in this order on the lower surface of the substrate 3, and further has a lower surface of the individual electrode 5. It has a transparent protective layer 11 on it.

The common electrode 4, the photoconductive film 2, and the transparent conductive film 6 are provided with a light guiding window 10 for guiding the light emitted from the light source 7 to the original 9.

The light emitted from the light source 7 passes through the light guide window 10 and reaches the document 9.
The light is reflected from the surface and reaches the photoconductive film 2. After this, the density distribution on the surface of the document 9 is converted into the strength of the current in the same manner as in the embodiment described above.

In this embodiment, a transparent protective layer 11 is provided to protect each member from contact with the original 9, and has a thickness of 3.
It is preferable that the thickness is about 15 μm, and the material thereof is Sin, AjZ2o3. st, N4, SiC, O
,N,,SiB,O,N,,5iBX O,-X.

S i AiX 0! -X% Taz os or the like may be used.Specific Effects of the Invention The image sensor of the present invention has a photoconductive film that is a thick film made of T1I.

Therefore, the response speed is fast and it can be suitably used for high-speed facsimile and the like.

Furthermore, since the photoconductive film has a single layer structure, it is easy to manufacture, and since it is formed by a thick film method such as screen printing, manufacturing costs can be kept low.

Furthermore, the photoconductive film made of T1I has good and stable characteristics, and also has uniform characteristics and has a high manufacturing yield.

The image sensor of the present invention having such effects can be suitably used for facsimiles and the like.

The present inventors conducted the following experiment in order to confirm the effects of the present invention.

[Experimental Example 1] 11 parts by weight of Tl having an average particle size of 0.5 μm, 0.5 parts by weight of ethyl cellulose, and 1 part by weight of terpineol were mixed to prepare a paste.

This paste was printed on a glass substrate by screen printing and heated at 300°C in a vacuum (IXIO-3 Torr).
A photoconductive film was formed by baking for 30 minutes.

The film thickness after firing was 10 μm.

This photoconductive film was sandwiched between opposing Cu electrodes as shown in FIG. 4 to form a photoelectric conversion element, and the relative sensitivity to light wavelength was measured.

Note that the Cu electrode was formed to a thickness of 1.5 μm by vapor deposition, and was formed into a predetermined pattern by wet etching.

Etchant: 20% H2S O4, 10% Cry
, an aqueous solution was used. Also, the etching rate is 2μ
It was m/lll1n.

The results are shown in FIG.

From the results shown in FIG. 7, it can be seen that the photoconductive film made of Tll has maximum sensitivity in the red region and can be suitably applied to an image sensor using a red light emitting LED.

For comparison, a photoconductive film made of T1I was formed to a thickness of 1 μm by vapor deposition, and a photoelectric conversion element was produced in the same manner as above. This device also had maximum sensitivity at the same wavelength as the photoelectric conversion element of the present invention, but its maximum sensitivity was
It was 40% of that of the present invention.

[Experimental Example 2] Using the photoelectric conversion element produced in Experimental Example 1, a 660 nm GaAJ2As red light emitting LED was used as a light source, and photocurrent with respect to light intensity was measured.

The results are shown in FIG.

As shown in FIG. 8, it is clear that in the photoconductive film made of T1I, the photocurrent increases almost linearly with respect to the light intensity, and it can be suitably used in an image sensor.

[Experimental Example 3] Using the photoelectric conversion element described above, the response speed (rise and fall) to light irradiation was measured.

As a light source, GaAjLAs-LEI)(λ, = 660
nm) was used.

The rise time was 0.2 m5 ec or less, and the fall time was 0.5 m5 ec or less.

The results show that the photoconductive film made of T1I has a fast optical response speed and can be suitably applied to high-speed facsimile and the like.

[Experimental Example 4] According to Experimental Example 1 above, an image sensor having the configuration shown in FIG. 4 was manufactured and its characteristics were measured.

The details and characteristics of this image sensor are shown in Figure 1 below.

Table 1 Number of elements 1728 pixels Element density 8 pixels/mm Light sensitivity 0.2 μA/1 x spectral sensitivity
660nm SN ratio 10:1 or more Inter-element variation ±10% or less Photoresponse speed 1m5ec or less In Table 1 above, the photosensitivity is when a red light emitting LED (wavelength 660nm) is used as a light source with an applied voltage of 10μ. , spectral sensitivity indicates the peak wavelength. Further, the S/N ratio is a binary value of black and white, and the light response speed is a value when the peak illuminance is 100 lux.

From the results shown in Table 1, the image sensor of the present invention has
It can be seen that the characteristics are good.

[Brief explanation of the drawing]

1 and 3 are plan views of preferred embodiments of the image sensor of the present invention, and FIGS. 2 and 4 are plan views of the image sensor shown in FIGS. 1 and 3, respectively.
1I line and rV-rV line sectional views. FIG. 5 is a longitudinal sectional view of another embodiment of the image sensor of the present invention, and FIG. 6 is a bottom view of the image sensor shown in FIG. 5. FIG. 7 is a graph showing the relationship between light wavelength and relative sensitivity, and FIG. 8 is a graph showing the relationship between light intensity and photocurrent. Explanation of symbols 1... Image sensor, 2... Photoconductive film, 3... Substrate, 4 Common electrode, 5... Individual electrode, 6... Transparent conductive film, 7... Light source, 8...・Optical system, 9... Original, 10... Light guiding window, 1! ...Transparent protective layer FIG, 1 FIG, 2 FIG, 3 FIG, 4' 9 Fl (3, 5, 7 FIG, 5 FIG, 7 wavelength (nm)

Claims (2)

[Claims] (1) An image sensor having a photoconductive film whose conductivity changes with the incidence of light, the photoconductive film being a thick film made of T1I. (2) The image sensor according to claim 1, wherein the light is emitted from a red light emitting LED.